@Psychronia The ma (é”) in maou is the same as the ma in mahou we use for stuff like magical girls, so both the "devil/demon king" and "magic" start with the same character, and it's being pulled from mazoku which is going to generally either turn out as "demons" or something like "magic clan/people." Majin is in basically the same boat, you can translate it a couple different ways because of the same ma character, primarily it'll be something like a "demon god" or "magician." Yet another example common to a series like this is translations basically flipping a coin on whether something is a demon beast or a magic beast, and I've also seen some instances of people not being sure if they were supposed to translate something as "demon sword" or "magic sword."
Long story short, é” is a pain in the ass and most of the translations of it you'll see on here are just shots in the dark based on the context until an official version is around to lock it in as one thing or another. Big ol' dang mess.
As far as I know it is not exactly that.
Demon King = devil = é”王
devil / evil spirit = é”
One way of saying "magic" in Japanese is
"magic" as in "witchcraft / sorcery" = 锿³•
So this term for "magic" just includes a term for "devil / evil sprit".
Hence "é”王" does primarily mean "demon king" / "devil" and might be able to mean "magic king" in a derived way depending on the context it is use in.